Figure 1.

Single-strand probe excess titrations of transcripts from two S. purpuratus Hox genes: SpHox3 (A) and SpHox11/13b (B). These examples are representative of the data sets that provided the measurements reported in this paper. Total RNA was extracted from unfertilized eggs and embryos at the indicated stages and in increasing amounts reacted with ³²P-labeled antisense RNA probes (see legend to Fig. 3 and Materials and Methods for probes and procedures). Transcript numbers were calculated from the slopes as described (20), taking into account the amount of total RNA per embryo (2.8 ng; ref. 22) and the lengths and specific activities of the probes.